Here’s how a large fancy color rough stone cracked during polishing, with a huge loss to the owner
In this article FCRF continues to raise awareness about issues that are generally hidden from the professional public. In a unique achievement, FCRF was able to get hold of a fully documented case in which the polishing of a high value stone went terribly wrong, with photos that illustrate each stage. This is an exceptional opportunity to illustrate the risks that manufacturers face and the possible gloomy outcome.
The beautiful 16.56 carat hexagon rough was bought In July 2016 at a diamond auction conducted by a Russian diamond producer. The stone had a very strong yellow saturation and was expected to yield a 9.5 carat vivid yellow cushion cut in a VS clarity grade.
The 16.56 Vivid Yellow Rough
Before beginning the polishing process, the stone was checked thoroughly for any internal tension it might have. The findings showedthat the stone had very low tension and therefore was safe to work on.
There are two reasons why a stone is examined for internal stress. The first is when a manufacturer wants to buy a processing insurance policy. The insurance company needs to determine whether it is willing to insure the diamond, its risk and the size of the premium to secure the process.
The second reason (regardless of the insurance process) is that stones that do show high internal stress are sometimes planned differently and do not go through a laser sawing process. In most cases a rough diamond is split into two parts, larger and smaller, in order to extract a second (smaller) stone from one of the apexes of the octahedron and increase the overall yield.
As this stone showed low stress, it was put into a laser sawing machine which successfully resulted in two parts, as shown in the picture.
The two parts after the laser sawing
The next step was to begin polishing the larger part.
Starting polishing the crown angels
At a certain point it was time to form the crown facets. The stone was safely glued to the dop* and the cutter placed the stone with a gentle motion on the polishing wheel. Knowing that this diamond cost just under a million dollars, he sensed a heavy responsibility. Every few seconds he lifted the stone up to inspect the progress of the facet with his loop. After a few strokes, he lifted the dop and could not believe his eyes… the clean vivid yellow stone that he had seen just seconds before had completely cracked, without any warning or sound.
The starting and end point of the crack
“I know it is difficult to comprehend but it feels as if a patient you are conducting a simple operation on died in your hands. Making the call to the owner of the diamond and letting him know he has lost a great deal of money is even worse,” said the polisher.
“The damage creates an enormous emotional blow. No one knows why a stone with low pressure cracks on the wheel. It’s a mystery. And there is no way to reverse it. If you break a very expensive porcelain Chinese vase you can glue it back together. If you punch a hole in a Rembrandt oil painting it can be restored, but if you crack a diamond there is no way to repair the damage,” the owner explained. He added that the polisher had been highly skilled and had used extreme caution.
At this point the only way to salvage some part of the investment was to split the stone on the crack and extract the maximum yield from the remaining pieces.
Splitting manually the cracked stone
When a yellow fancy color stone is reduced in size it loses its color. The reason for this lies in the fact that in a smaller stone light waves encounter less nitrogen molecules than they would have in a larger stone. The smaller pieces will generate a much weaker color than the original vivid yellow stone would have shown. As such, the outcome for the owner is an exponential loss on two counts – smaller sizes and weaker color.
The two parts of Rough after splitting the diamond
In the end, as seen in the images below, the 16.56 carat rough stone which was supposed to yield a 9.5 carat vivid yellow cushion, resulted in two diamonds in a “fancy yellow” grade of 2 and 3 carats each, at a value of one-tenth of the investment.
The end result yielded two Fancy Yellow Diamonds
In conclusion, we have tried to illustrate just one of the hardships faced by manufacturers of fancy color diamonds. There are many challenges to meet before the best stone is set in a luxurious piece of jewelry. Not least of these is the need to traverse the globe to source the diamonds. However, cracking a diamond is definitely the most painful of them all.
*Dop – a tool for holding gemstones for cutting or polishing.